As a method for achieving a lower bit cost of nonvolatile semiconductor memory devices and improving memory performance, scaling-down of memory cells is effective. However, scaling-down of memory cells has become technically difficult.
Thus, it has been proposed to use organic molecules in charge storage layers. Using various synthesized various molecular structures or substituents, desired electrochemical properties can be imparted to organic molecules. Since structural unit of organic molecule is small, the thickness and width of charge storage layers can be reduced, and thus scaling-down of memory cells can be achieved.
Fabrication of memory cell using three-dimensional stacked structure is one of the methods for achieving a lower bit cost of nonvolatile semiconductor memory devices. When three-dimensional stacked structure a memory cell arrangement is made three-dimensional, by thinning the total film-thickness of a memory cell, a higher density of memory cells can be achieved. Thus, for example, it is required to reduce the thickness of insulating layers such as a tunnel insulating film and a block insulating film. When a tunnel insulating film is made thinner, degradation in charge retention characteristics due to an increase in leak current becomes a problem.